ACAPULCO, Mexico — What was supposed to be a tight state election turned into a rout for the Democratic Revolution Party, boosting Mexico’s main leftist party’s chances for the presidency in 2006.

Running behind former Acapulco Mayor Zeferino Torreblanca, the party on Sunday ended 76 years of rule by the Institutional Revolutionary Party, or PRI, in the Pacific coast state of Guerrero.

With 92 percent of the vote counted, Torreblanca had a 55 to 42 percent lead over the PRI’s Hector Astudillo — embarrassing several respected polling companies who had the men in a statistical tie before the election.

Thousands of celebrating Democratic Revolution supporters danced in Acapulco’s main plaza early Monday as others cruised past tourists on the Costera boulevard honking horns and waving yellow party flags.

In a post-midnight news conference Torreblanca — who made his money on real estate investments — promised to govern “for the poorest of Guerrero, for our indigenous brothers, for the women and for all the others.”

Two other state elections Sunday went as predicted: Democratic Revolution held onto the governorship of Baja California Sur, where the resorts of Los Cabos are located, while the PRI held on to Quintana Roo, the site of Cancun.

Bittersweet victoryGuerrero was an unusually emotion-filled victory for Democratic Revolution, which was born in 1989 out of a merger of leftist parties and PRI dissidents. The party says 300 of its activists have been killed since then in the state for political motives.

It also improves the presidential chances of the party’s most popular figure, Mexico City Mayor Andres Manuel Lopez Obrador.

He has led nearly all recent polls for the upcoming national election, but his party finished third in the last two presidential votes and until now governed only three states on its own. The party’s weakness has cast doubts on its ability to win a nationwide campaign.

“It gives us a strong push toward 2006, without any doubt,” said party President Leonel Godoy.

President Vicente Fox’s National Action Party showed that it is not yet a true nationwide force. It managed barely 1 percent of the vote in Guerrero, 10 percent in Baja California Sur and finished third in Quintana Roo.

Stinging rebuke to PRI
The loss stung the PRI, which has been on the rebound since the shock of losing the presidency in 2000.

The party won seven of 10 state elections last year, though several were by tight margins. The victories had improved the presidential hopes of party President Roberto Madrazo — and his rivals in the party are sure to see the heavy loss in Guerrero as ammunition against him.

Both major parties here complained that opponents were using threats and violence to intimidate voters. The state is famed for tourist resorts such as Acapulco and Zihuatenejo, but its rugged mountains have spawned poverty, violence, guerrilla bands and heavy-handed political repression.

Attacks near Acapulco
On Saturday when unidentified gunmen with automatic weapons killed three policemen and a 15-year-old bystander in three separate guerrilla-style attacks in the Acapulco area, Democratic Revolution’s campaign coordinator, Julio Ortega, virtually accused the PRI of murder, saying the attack was part of the PRI’s campaign to intimidate voters.

In Quintana Roo state on Mexico’s other coast, former Cozumel Mayor Felix Gonzalez of the PRI defeated former Cancun Mayor Ignacio Garcia Zalvidea of Democratic Revolution. Addy Joaquin Coldwell, sister of a former PRI governor, was representing President Vicente Fox’s National Action Party.